The background of the invention will be discussed in two parts:
1. Field of the Invention
This invention relates to a keratometric device, and more particularly to a keratometric device for attachment to a binocular surgical microscope for use in observing and measuring the spherical surface of a cornea.
2. Description of the Prior Art
During ophthalmic surgery, for example surgery involving cataracts, ideally it is desirable to reconfigure the cornea after the operation to the same radius of curvature existing prior to the operation. In the human eye, the radius of curvature vaaries from individual to individual with a normal range being between forty and fifty diopters which correspond to radii of curvature of 8.44 millimeters to 6.75 millimeters respectively. In order to ascertain the radius of curvature prior to the operation, the surgeon would normally take measurements, in the office, along certain angles or meridians. Such prior art measurement techniques involve the use of telescopic instruments known as ophthalmometers or Keratometers. This information relating to the radius of curvature of the cornea will then become a part of the patient's history file. The operation would then be performed and on the next office visit after the operation, the patient's eye would then be remeasured to determine what effect the operation had on the radius of curvature.
A corneal measurement technique is shown and described in U.S. Pat. No. 3,895,860 and a keratometer device is referred to in U.S. Pat. No. 3,972,602.
U.S. Pat. No. 4,157,859 issued June 12, 1979 to Clifford Terry for a "Surgical Microscope System." The microscope system of this patent depicts an advanced system and method for enabling a surgeon to observe the changes of radius of curvature during suturing of the incision required for cataract operations. With this system, a binocular microscope is employed, the microscope having means for projecting an image onto the cornea, the image preferably being a circle created by a ring lamp surrounding the microscope body adjacent the objective lens. A pair of prisms are mounted on a slidable tray member for partially intercepting each of the two light paths through the microscope, the prism powers being selected for creating two virtual images in a predetermined relation to each other and to the real image.
In measuring the radius of curvature of the cornea, the zoom mechanism is adjusted until the two formed images viewable through the microscope are in tangential relation with the real image with the zoom power being proportional to the radius of curvature provided on a display in diopters of power. A complete discussion of the principles and operation, as well as structure of the surgical microscope system of U.S. Pat. No. 4,157,859 may be had by reference thereto, that description being fully incorporated herein by this reference.
In the microscope system of U.S. Pat. No. 4,157,859, the prisms for creating the formed images are placed into the optical path immediately below the binocular assembly and above the zoom mechanism. This particular construction was facilitated by virtue of the construction of the Zeiss OPMI6 microscope which has a detachable eyepiece assembly with the body being configured for receiving other devices in modular form. Other surgical microscopes utilized by ophthalmic surgeons, however, are not modularly configured, and the utilization of the system of that patent in such other microscopes would require reconstruction of major parts of the microscope.
It is accordingly an object of this invention to provide a new and improved keratometric device.
It is another object of this invention to provide a new and improved keratometric device for use with a binocular surgical microscope.
It is a further object of this invention to provide a new and improved keratometric device which may be simply and economically fitted to existing surgical microscopes.